In one known method for the disposal of radioactive waste, the waste is placed in boxes and then covered with a cementitious grout which is injected into the box. After a curing period, a capping grout is introduced into the box in order to seal the waste and to remove any ullage space where gases can accumulate. After a further curing period, a lid is fixed to the box, which is then subjected to a decontamination process. The boxes are transferred to a heavily-shielded storage building where they are deposited in rows of vertical stacks by a remotely-operated crane.
In an alternative storage system, the waste is encapsulated in a cementitious matrix inside a stainless steel drum. Several drums are placed in a stillage and the stillages are formed into a vertical stack using a remotely-operated crane.
The boxes or stillages may have to be stored for a very long period of time of, say, 100 years. During that period, it is desirable that the storage building and stacks of boxes or stillage are able to withstand not only operational loads, but also seismic and other extreme environmental conditions.
It is an object of this invention to provide apparatus for storing hazardous material in which a stack of containers holding the material remains stable when subjected to external forces, such as those generated during a seismic event.